Novell has announced the release of Mono version 1.2, a new version of the Mono project to create an implementation of the Microsoft .Net Framework for open source. Mono 1.2 enhances the open-source effort and is a major step toward compatibility with the .Net Framework 2.0, Novell officials said. Novell announced the new version on Nov. 9 at the Microsoft TechEd Developers conference in Barcelona.

So I've taken a little utility I've written on Windows and tries to run it (using the already compiled assembly).
It worked, although mono doesn't seem to implement the AutoSize property for labels.

I then tried to compile the application using mono. Unfortunately I got plenty of errors.

MainForm.cs(32,4): error CS0117: `System.Windows.Forms.Application' does not contain a definition for `SetCompatibleTextRenderingDefault'
MainForm.Designer.cs(75,4): error CS0117: `System.Windows.Forms.ListBox' does not contain a definition for `FormattingEnabled'
MainForm.Designer.cs(100,4): error CS0117: `System.Windows.Forms.Button' does not contain a definition for `UseVisualStyleBackColor'
MainForm.Designer.cs(112,4): error CS0117: `System.Windows.Forms.Button' does not contain a definition for `UseVisualStyleBackColor'
MainForm.Designer.cs(135,4): error CS0117: `System.Windows.Forms.Button' does not contain a definition for `UseVisualStyleBackColor'
MainForm.Designer.cs(158,4): error CS0117: `System.Windows.Forms.Button' does not contain a definition for `UseVisualStyleBackColor'
MainForm.Designer.cs(163,4): error CS0117: `FolderMerger.MainForm' does not contain a definition for `AutoScaleDimensions'
MainForm.Designer.cs(164,25): error CS0234: The type or namespace name `AutoScaleMode' does not exist in the namespace `System.Windows.Forms'. Are you missing an assembly reference?
MainForm.Designer.cs(164,4): error CS0117: `FolderMerger.MainForm' does not contain a definition for `AutoScaleMode'

To be honest, I built this application on SharpDevelop, using the .NET 2.0 framework. However, I haven't (to my knowledge) used any .NET 2.0 abilities in my application (if these error messages say otherwise, please correct me).

So I'm afraid that Mono is not quite there yet. To me it still seems that Windows.Forms is incomplete.

As you've seen you've used NET 2.0 features. Some of those are even implemented in Mono under 2.0 profile. (you could try compiling with gmcs)
Anyway Mono 1.2 does not officially support NET 2.0 features. It may sometimes work but it's not supported.